The field of art of the present invention includes various diagnostic or analytic test procedures such as those involving qualitative and quantitative analysis in which a number of steps must be consecutively performed in order to get a proper final measurement. An exemplary test procedure of this type is radioimmunoassay where very small volumetric additions of various reagents, on the order of 100 microliters, must be added to standard dilutions of a patient's sample to determine the presence and quantity of certain proteins such as growth hormone, or immunoglobulins associated with allergic reactions or parasitic infections. Prior to immunoassay two of the methods for measuring small quantities of materials were bioassays and radial diffusion.
As explained more fully in an article entitled "Principles of Radioimmunoassay" written by Dr. James McQuire (48 Mayo Clin. Proc. at 637, Sept., 1973), radioimmunoassay provides a method for measurement of small quantities of substances not measurable by other techniques. The techniques of immunoassay have been applied to a number of substances of various structures. The technique evolved from work with the insulin system: insulin resistance was being investigated, antibodies to insulin were identified, then antibodies to insulin were subsequently produced, and a method was developed whereby very small quantities of insulin could be measured by application of these antibodies. These techniques have now been applied to a wide variety of both large and small, principally organic, molecules.
In a radioimmunoassay, antibodies to the substance being measured are necessary. These are generally produced by hyperimmunization of experimental animals. In addition, the antibodies must have high affinity for the substance being measured.
Besides the antibody of high affinity, a radiolabeled detector substance is utilized. The antibody molecules need not be specific if the detector is specific; therefore, it is possible to immunize with rather crude materials. Some radiolabeled materials currently used are tagged with either .sup.131 I, .sup.125 I, or .sup.3 H. The radiolabeled substance must be pure, and there must be a standard to make comparisons. The major requisite necessary in the radioimmunoassay system is a method of separating antibody-free radioactivity from antibody-bound radioactivity.
In the radioimmunoassay procedure, the concentrations of antibody and of radioactive labeled material in the tube are kept constant. A standard curve is prepared by using known amounts of the substance to be measured. The ordinate value can be expressed in a variety of ways, as percent precipitated or bound: free ratio (B/F) or any expression of these themes. There is a relationship between the amount of unlabeled material which was in the tube and the amount of proportion of radioactivity which is precipitated. This standard curve, therefore, permits one to determine the amount of the selected protein in an unknown sample from knowing the percent of radioactivity precipitated.
In the prior art procedure it was necessary for the technician running the procedure to either keep records to indicate where he or she was in the procedure or to run the test procedure in one session which, very often, ran 5 hours or more. However, often in running such a test procedure the technician was interrupted or for some other reason lost track of where he or she was in the procedure. The present invention is designed to eliminate that problem.